Tractor scraper apron drive

ABSTRACT

A tractor scraper includes a tractor portion and a scraper portion. The scraper portion may include a bowl and an apron disposed adjacent a forward end of the bowl. The tractor scraper may also include a drive configured to raise the apron. The drive may include an actuator drivingly connected to a pinion. The drive may also include a rack connected to the apron and the pinion in a manner allowing the actuator to raise the apron by driving the rack with the pinion. The rack may be connected to the apron in a manner allowing relative movement between the rack and the apron.

TECHNICAL FIELD

The present disclosure relates to tractor scrapers and, more particularly, to drives for raising and lowering aprons on tractor scrapers.

BACKGROUND

Tractor scrapers typically include a tractor portion connected to a scraper portion for scraping and transporting material (e.g., soil) from a terrain surface. The scraper portion of a tractor scraper generally includes a bowl with a floor and sides, as well as a blade adjacent a forward end of the floor of the bowl. Such a tractor scraper typically scrapes and gathers material from the terrain surface by driving forward with the blade engaged to the terrain surface and a forward portion of the bowl at least partially open, such that material scraped from the terrain surface by the blade travels across the top of the blade, through the opening in the front of the bowl, onto the floor of the bowl.

To control intake and discharge of material through the front of the bowl, a tractor scraper typically also includes an apron disposed between the sides of the bowl at a forward portion of the bowl, as well as a drive for raising and lowering the apron to either close or open the forward portion of the bowl. For example, U.S. Pat. No. 3,016,633 to Le Tourneau (“the '633 patent”) discloses a tractor scraper with such an apron and drive system disposed adjacent a forward end of the bowl. The apron disclosed in the '633 patent has its sides pivotally engaged to the sides of the bowl, and the drive for the apron pivots the apron upward or downwardly to open or close the front of the bowl.

The drive for the apron in the '633 patent has a rack-and-pinion design. The rack of the system is a semicircular gear fixed on the front face of the apron in a position concentric with the pivot joints connecting the apron to the bowl. The pinion sits adjacent the front face of the apron in a position where teeth of the pinion engage teeth of the rack. As a motor rotates the pinion, the pinion drives the rack upward or downward, thereby pivoting the rack and the apron upward or downward about the pivot joints connecting the apron to the bowl. Because the rack is positioned concentric to the pivot joints, each portion of the rack passes through the same point adjacent the pinion as the apron and rack move upward or downward. This maintains the teeth of the rack engaged to the teeth of the pinion while the apron and rack move upward and downward.

While the '633 patent discloses a drive for moving the apron of a tractor scraper up and down, the configuration of the system shown in the '633 patent may have certain disadvantages. For example, with the apron pivotally mounted to the bowl and the rack fixedly attached to the front face of the apron, proper functioning of the drive may require the disclosed semicircular shape and concentric mounting of the rack to keep the rack properly engaged to the pinion over the full range of motion of the apron. These restrictions may have some drawbacks. For example, a semicircular shape of the rack may drive more cost and complexity in the processes of manufacturing the rack. Additionally, the configuration of the rack and pinion disclosed by the '633 patent may require tight tolerances in the manufacturing of the apron and the components for mounting it, so that the front face of the apron moves through a precise path to also ensure that the rack remains properly engaged to the pinion through the full range of motion of the rack. These requirements may also increase the cost and complexity of manufacturing the apron and the tractor scraper.

The system and methods of the present disclosure may help address these disadvantages.

SUMMARY

One disclosed embodiment relates to a tractor scraper. The tractor scraper may include a tractor portion and a scraper portion. The scraper portion may include a bowl and an apron disposed adjacent a forward end of the bowl. The tractor scraper may also include a drive configured to raise the apron. The drive may include an actuator drivingly connected to a pinion. The drive may also include a rack connected to the apron and the pinion in a manner allowing the actuator to raise the apron by driving the rack with the pinion. The rack may be connected to the apron in a manner allowing relative movement between the rack and the apron.

Another embodiment relates to a method of operating a tractor scraper. The tractor scraper may have a tractor portion and a scraper portion. The scraper portion may include a bowl and an apron disposed adjacent a forward portion of the bowl. The method may include raising the apron to open the forward portion of the bowl, which may include driving a pinion with an actuator, driving a rack with the pinion, and raising the apron with the rack while allowing relative movement between the rack and the apron.

A further disclosed embodiment relates to a tractor scraper, which may include a tractor portion and a scraper portion. The scraper portion may include a bowl and an apron with a forward face disposed adjacent a forward end of the bowl. The tractor scraper may also include a drive configured to raise the apron to open the forward end of the bowl. The drive may include an actuator drivingly connected to the pinion. The drive may also include a rack connected to the apron and the pinion in a manner allowing the actuator to raise the apron by driving the rack with the pinion. A shape of the rack may differ from a shape of a vertical cross-section of the forward face of the apron.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one embodiment of a tractor scraper according to the present disclosure;

FIG. 2 shows a perspective view of one embodiment of a forward portion of a scraper portion of a tractor scraper according to one embodiment of the present disclosure;

FIG. 3 shows a vertical cross-section of a forward portion of the scraper shown in FIG. 2;

FIG. 4 shows a close view of a portion of the contents of FIG. 2; and

FIG. 5 is a schematic illustration of one embodiment of a system for powering and controlling an apron drive according to the present disclosure.

DETAILED DESCRIPTION

FIG. 1 shows a tractor scraper 10 according to one embodiment of the present disclosure. Tractor scraper 10 may include a tractor portion 12 and a scraper portion 14. Tractor portion 12 may have a propulsion system for propelling tractor scraper 10. For example, tractor portion 12 may have traction devices 18 (one shown) operably connected to one or more power sources for driving propulsion devices 18 to propel tractor portion 12. Traction devices 18 may include any type of components operable to transmit power to a terrain surface 15 underlying tractor scraper 10 to propel it, including, but not limited to, wheels (as shown in FIG. 1) and/or track units. The power sources driving traction devices 18 may include, but are not limited to, one or more engines, transmissions, electric motors, and/or hydraulic motors. Tractor portion 12 may also include an operator's station 20 where an operator may control various aspects of the operation of tractor scraper 10.

Scraper portion 14 may be connected to tractor portion 12 in such a manner that scraper portion 14 moves across terrain surface 15 in concert with tractor portion 12. For example, scraper portion 14 may connect to tractor portion 12 via an articulating hitch 16. Tractor scraper 10 may have various provisions for suspending a rear portion of scraper portion 14 from terrain surface 15. For example, scraper portion 14 may include wheels 32 for supporting a rear portion of scraper portion 14 from terrain surface 15. Alternatively, scraper portion 14 may include one or more track units, skids, or similar components for supporting the rear portion of scraper portion 14 from terrain surface 15.

To suspend the forward portion of scraper portion 14, tractor scraper 10 may include arms 17 (one shown). A forward end of each arm 17 may connect to hitch 16, and a rearward end of each arm 17 may pivotally connect to scraper portion 14 ahead of wheels 32.

In some embodiments, scraper portion 14 may also include provisions for assisting tractor portion 12 in propelling tractor scraper 10. For example, in some embodiments, scraper portion 14 may include one or more power sources driving wheels 32 to assist in propelling tractor scraper 10.

Scraper portion 14 may be configured to gather and haul matter (e.g., soil) from terrain surface 15. Scraper portion 14 may include a bowl 22 for receiving and hauling the gathered matter. FIGS. 2 and 3 illustrate portions of bowl 22 and other components of scraper portion 14 in greater detail. FIG. 2 provides a perspective illustration of a forward portion of scraper portion 14, and FIG. 3 is a sectional view showing a vertical cross-section of the forward portion of scraper portion 14. As shown in FIG. 2, bowl 22 of scraper portion 14 may include a right side 24 and a left side 26. A spreader member 47 may extend between and connect a front portion of right side 24 and a front portion of left side 26. As shown in FIG. 3, bowl 22 may include a floor 28 which may extend between right side 24 and left side 26. At a forward end of floor 28, scraper portion 14 may include a blade 30 for scraping material from terrain surface 15 onto floor 28 of bowl 22 as tractor scraper 10 moves forward. Tractor scraper 10 may have one or more actuators operable under the control of the operator of tractor scraper 10 to raise and lower the front portion of bowl 22 and blade 30 relative to terrain surface 15.

Between forward ends of right side 24 and left side 26 of bowl 22, scraper portion 14 may include an apron 34. As shown in FIG. 2, apron 34 may include a forward face 36 that extends laterally between right side 24 and left side 26 of bowl 22. Apron 34 may also include a left apron side 38 attached to forward face 36 adjacent left side 26 of bowl 22. Left apron side 38 may be pivotally connected to left side 26 of bowl 22 at a pivot joint 40, so that left apron side 38 and forward face 36 may pivot about pivot joint 40. A right apron side (not shown) may connect to forward face 36 adjacent right side 24 of bowl 22, and the right apron side may connect to right side 24 of bowl 22 via another pivot joint aligned with pivot joint 40, such that apron 34 may pivot about a lateral axis 41 extending through these pivot joints.

As shown in FIG. 3, the vertical cross-section of forward face 36 of apron 34 may extend rearward as it extends down toward blade 30. In some embodiments, one or more portions of the vertical cross-section of forward face 36 may be curved, such as a lower portion 42 of the configuration shown in FIG. 3. Such curved portions may or may not have a semicircular shape concentric with axis 41. In some embodiments, one or more portions of the vertical cross-section of forward face 36 may be straight, such as an upper portion 44 of the embodiment shown in FIG. 3.

Tractor scraper 10 may include a drive 46 for raising and lowering apron 34 to either open or close a forward portion of bowl 22 above blade 30. Drive 46 may be a rack-and-pinion type drive having a rack 48, a pinion 50, and an actuator 52 for driving the pinion 50. The components of drive 46 may be mounted to various parts of tractor scraper 10. In some embodiments, rack 48, pinion 50, and actuator 52 may all be fully mounted to scraper portion 14. For example, as shown in FIGS. 2 and 3, actuator 52 and pinion 50 may be mounted to a mast 49 extending upward and somewhat rearward from spreader member 47, and rack 48 may extend between apron 34 and pinion 50. Rack 48 may be an elongated member having a plurality of teeth 54 extending along one side thereof. Pinion 50 may be a rotary member having a plurality of teeth 56 engaging teeth 54 of rack 48. Actuator 52 may include any component or components operable to rotate pinion 50 to advance rack 48 in the direction in which teeth 54 extend along rack 48. In some embodiments, actuator 52 may include a rotary motor (such as a hydraulic motor) by itself or in combination with one or more gear-reduction units or other power-transmission components. Exemplary provisions for powering actuator 52 will be discussed in greater detail below in connection with FIG. 5.

To allow drive 46 to move apron 34 by driving rack 48, apron 34 may be connected to rack 48. In some embodiments, rack 48 may connect to apron 34 in a manner allowing relative movement between apron 34 and rack 48 when drive 46 moves apron 34 up and down. For example, a lower end of rack 48 may be pivotally connected to a bracket 58 attached to forward face 36 of apron 34, such that pivotal relative movement may occur between apron 34 and rack 48 as drive 46 moves rack 48 to raise and lower apron 34. In some embodiments, such a pivotal connection may be effected via a pin 61 connecting the lower portion of rack 48 to bracket 58.

With rack 48 connected to apron 34 in a manner allowing relative movement between the two components, tractor scraper 10 may include additional provisions for restraining the motion of rack 48 to maintain its teeth 54 engaged to the teeth 56 on pinion 50. For example, as best shown in FIGS. 3 and 4, tractor scraper 10 may include a retainer 65 disposed adjacent a face 62 of rack 48 opposite pinion 50, so that the portion of rack 48 adjacent pinion 50 is sandwiched between pinion 50 and retainer 65. Retainer 65 may include a projection extending parallel to an axis of rotation of pinion 50. Face 62 of rack 48 may ride on a flat surface of retainer 65. Retainer 65 may be attached to a bracket 64 on scraper portion 14. The attachment of retainer 65 to bracket 64 may be such that retainer 65 is allowed some movement with respect to bracket 64. For example, retainer 65 may be allowed to move along a slot 66 of bracket 64. Slot 66 may be, for example, a semicircular slot concentric with the axis of rotation of pinion 50. The purpose of this movement of retainer 65 will be discussed in greater detail below.

In addition to preventing rack 48 from moving away from pinion 50 in directions perpendicular to the axis of pinion 50, retainer 65 may also limit movement of rack in directions parallel to the axis of pinion 50. For example, retainer 65 may include a shoulder 68 that abuts one side of rack 48, as well as a similar shoulder abutting the opposite side of rack 48. Additionally, pinion 50 may include annular rings 70, 72 abutting opposite sides of rack 48 to help restrain rack 48 in directions parallel to the axis of pinion 50. Retainer 65 may have different configurations than that shown in FIGS. 3 and 4. For example, in some embodiments, retainer 65 may include a roller on which face 62 of rack 48 may ride.

Rack 48 may have various shapes and may be oriented in various manners. In some embodiments, the shape of rack 48 may differ from the shape of the vertical cross-section of forward face 36 of apron 34. For example, as shown in FIG. 3, rack 48 may have a substantially straight shape (i.e., may extend along a substantially straight longitudinal axis), whereas the vertical cross-section of forward face 36 of apron 34 may bend and/or curve at one or more points. As also shown in FIG. 3, in some embodiments, teeth 54 of rack 48 may face substantially rearward. Alternatively, some embodiments of rack 48 may be curved. One possible design of such a curved rack 48 is discussed in greater detail below.

FIG. 5 schematically illustrates one embodiment of components that tractor scraper 10 may have for powering and controlling drive 46 to control the position of apron 34. In the example shown in FIG. 5, actuator 52 is a reversible, variable displacement hydraulic motor drivingly connected to pinion 50, and tractor scraper 10 includes a hydraulic system and controls for providing a flow of hydraulic fluid to actuator 52 to drive pinion 50. The components of FIG. 5 for producing a flow of hydraulic fluid for actuator 52 include a reversible, variable-displacement hydraulic pump 74 driven by a power source 76, as well as a hydraulic valve 78 for controlling an amount and a direction of hydraulic fluid flow from the reversible, variable-displacement pump 74 to actuator 52. Power source 76 may be any type of component operable to mechanically drive hydraulic pump 74, including, but not limited to, an internal combustion engine, an electric motor, and a hydraulic motor.

FIG. 5 also schematically illustrates an operator input device 80 and a controller 82 for controlling actuator 52, reversible, variable-displacement hydraulic pump 74, hydraulic valve 78, and power source 76. Operator input device 80 may be any type of component configured for an operator to command up or down movement of apron 34. For example, as shown in FIG. 5, operator input device 80 may be a switch connected to an operator control handle, which may be located at the operator's station 20 of tractor scraper 10. Operator input device 80 may be operatively connected to controller 82 such that operator manipulation of operator input device 80 to command up or down movement of apron 34 is communicated to controller 82. Controller 82 may be any type of device operable to receive operator commands to move apron 34 and control one or more other components of tractor scraper 10 to activate actuator 52 to provide the commanded up or down apron movement. In some embodiments, controller 82 may include one or more microprocessors (not shown) and/or one or more memory devices (not shown). Controller 82 may be operatively connected to actuator 52, reversible, variable-displacement hydraulic pump 74, power source 76, and/or hydraulic valve 78. Controller 82 may be configured (e.g., programmed) to control these components to provide operation of actuator 52 consistent with operator commands for up and down movement of apron 34.

A tractor scraper 10 according to the present disclosure is not limited to the exemplary configuration shown in FIGS. 1-5. For instance, rack 48 may have a different configuration and may connect to apron 34 in a different manner. Similarly, tractor scraper 10 may have a different configuration of components for holding rack 48 in engagement with pinion 50. Additionally, actuator 52 may be a different kind of component. For example, in some embodiments, actuator 52 may be a fixed-displacement hydraulic motor, instead of a variable-displacement hydraulic motor. In some embodiments, actuator 52 may be a type of component other than a hydraulic motor, such as an electric motor. Additionally, tractor scraper 10 may have different components than those shown in FIG. 5 for providing power to actuator 52 and/or controlling actuator 52. For example, pump 74 may be fixed-displacement and non-reversible.

Furthermore, in addition to rack 48, pinion 50, and actuator 52, tractor scraper 10 may include one or more additional components for assisting movement of apron 34. For example, tractor scraper 10 may include one or more additional rack and pinion assemblies for assisting movement of apron 34. Furthermore, apron 34 may have a different configuration than shown in the figures and/or apron 34 may be connected to tractor scraper 10 in manners other than through pivot joints 40 connecting apron 34 to sides 24, 26 of bowl 22. Similarly, bowl 22 may have a different configuration than shown in the figures. Additionally, tractor scraper 10 may have different configurations of components for raising and lower the front portion of bowl 22, for connecting scraper portion 14 to tractor portion 12, for suspending the rear of scraper portion 14, and/or for propelling tractor scraper 10.

INDUSTRIAL APPLICABILITY

Tractor scraper 10 may have use in any situation where it may prove useful to scrape material from a terrain surface and collect the material in bowl 22. Apron 34 and drive 46 for moving it may have use in any situation where it may prove helpful to use apron 34 to control intake and discharge of material from the forward end of bowl 22 by closing or opening the forward portion of bowl 22. In many circumstances, an operator of tractor scraper 10 may initially activate drive 46 to raise apron 34 as high as it will go to create an opening in the forward portion of bowl 22 between a lower edge of apron 34 and blade 30 of bowl 22. Subsequently, the operator may lower blade 30 to engage terrain surface 15 and drive tractor scraper 10 forward, so that blade 30 scrapes material from terrain surface 15 and the material scraped from terrain surface 15 accumulates on floor 28 of bowl 22. After at least some material has accumulated in bowl 22, the operator may activate drive 46 to lower apron 34 to reduce or close the opening in the forward portion of bowl 22 to retain the accumulated material in bowl 22 with apron 34. The operator may also raise blade 30 to disengage it from terrain surface 15. Subsequently, the operator may drive tractor scraper 10 to another location, activate drive 46 to raise apron 34 to at least partially open the forward portion of bowl 22. With the apron 34 leaving the forward portion of bowl 22 at least partially open, the operator may then discharge material from bowl 22 through the opening at the forward portion of bowl 22.

The operator may command upward or downward movement of apron 34 with operator input device 80. If the operator manipulates operator input device 80 to request upward movement of apron 34, controller 82 may receive this command and adjust the operation of reversible, variable-displacement hydraulic pump 74 and/or hydraulic valve 78 to power actuator 52 to rotate pinion 50 to drive rack 48 upward. For example, in the configuration shown in FIG. 3, actuator 52 may rotate pinion 50 counterclockwise (from the direction viewed in FIG. 3), so that teeth 56 on the forward side of pinion 50 push upward on the meshed teeth 54 of rack 48 to drive rack 48 generally upward. With pinion 50 pushing up on rack 48, rack 48 may pull on apron 34 via pin 61 pivotally engaged to bracket 58. By pulling up on bracket 58, rack 48 may tend to lift forward face 36 of apron 34, such that apron 34 may rotate upward around pivot axis 41 on pivot joints 40.

As pinion 50 drives rack 48 generally upward and apron 34 rotates upward around axis 41, rack 48 may move upward between pinion 50 and retainer 65. At the same time, the angular orientation of rack 48 relative to vertical and relative to apron 34 may change. As apron 34 rotates upward around axis 41, bracket 58 and pin 61 may move both horizontally and vertically, changing the angular relationship between the position of pin 61 and pinion 50, thereby changing the angular relationship between the lower end of rack 48 and the portion of rack 48 engaged to pinion 50. As this occurs, retainer 65 may automatically respond by sliding within slot 66 to accommodate the changing angular orientation of rack 48 while retaining rack 48 sandwiched between retainer 65 and pinion 50, so that teeth 54 of rack 48 remain properly engaged to teeth 56 of pinion 50. Alternatively, in some such embodiments, rack 48 may be curved in a manner such that, when the pinion 50 drives the rack 48 upward and downward and the position of pin 61 moves relative to pinion 50, the portion of the rack 48 engaged to the pinion 50 always maintains the same angular relationship relative to the pinion 50. This may allow omitting slot 66 and fixing retainer 65 in one position. During lowering of apron 34 by driving rack 48 generally downward, pivot pin 61, pinion 50, and retainer 65 may similarly function to allow rack 48 to slide and rotate in directions opposite which rack 48 did on the ascent.

Thus, the disclosed embodiments allow considerable movement of rack 48 relative to apron 34 while maintaining rack 48 engaged between apron 34 and pinion 50 in a manner allowing rack 48 to transmit lifting or lowering force to apron 34. This may allow maintaining pinion 50 drivingly connected to apron 34 via rack 48 through a wide range of upward and downward movement of apron 34, regardless of the positional relationship between forward face 36 of apron 34 and pinion 50. This may provide significant freedom in the design of the shape of apron 34 and the manner in which it attaches to and moves relative to tractor scraper 10. It may also accommodate substantial variation in the position of the apron 34 at various points during the lifting cycle, which may help suppress manufacturing cost and complexity by allowing use of relatively looser tolerances in the manufacture and assembly of apron 34 and pivot joints 40. This may also facilitate retrofitting a drive 46 according to the present disclosure to a tractor scraper 10 that originally included a different apron drive, as the drive 46 of the present disclosure may be able to accommodate relatively loose tolerances that may have been used in manufacturing and mounting the apron 34 of such an existing tractor scraper.

The disclosed configurations of drive 46 may also afford substantial freedom in designing the shape of rack 48. This may allow the designer to select a configuration of rack 48 that provides low manufacturing cost and complexity, as well as durability. For example, a rack 48 that has a substantially straight longitudinal axis like that shown in FIGS. 2-5 constitutes one design that may offer relatively low manufacturing cost and complexity, as well as relatively high durability. Furthermore, the disclosed manners of connecting rack 48 between apron 34 and pinion 50 may allow drive 46 to continue functioning properly even if rack 48 suffers some deformation in operation.

The disclosed configurations may also help avoid plugging of teeth 54 on rack 48 with material (e.g., soil) scraped from terrain surface 15. Facing teeth 54 of rack 48 rearwardly may help shield them from any material collecting in front of rack 48 as tractor scraper 10 moves forward. By helping to keep teeth 54 clean, this configuration may promote reliable operation and durability of drive 46.

The disclosed embodiments also have other advantageous features. For example, mounting actuator 52, pinions 50 and rack 48 all on the scraper portion 14 of tractor scraper 10 may provide certain benefits. In particular, placing these components of drive 46 all on scraper portion 14 may ensure that relative movement between scraper portion 14 and tractor portion 12 does not create unintended movement of apron 34 relative to bowl 22. This may help keep the task of controlling the position of apron 34 simple.

Operation of the tractor scraper 10, apron 34, and drive 46 is not limited to the examples discussed above. For instance, rack 48 may move in different manners relative to apron 34 and/or pinion 50. For example, rather than only pivoting about pin 61 relative to apron 34, in some embodiments, rack 48 may also translate in one or more directions relative to apron 34. Similarly, apron 34 may move in different manners than discussed. Additionally, tractor scraper 10 may provide hydraulic fluid to actuator 52 with different components than those shown in FIG. 5. Alternatively, in embodiments where actuator 52 is not a hydraulic motor, tractor scraper 10 may employ means other than hydraulic components to power actuator 52. For example, where actuator 52 is an electric motor, tractor scraper 10 may use electrical components to power actuator 52. Furthermore, tractor scraper 10, apron 34, and drive 46 may be controlled other than by a human operator on tractor scraper 10. For example, these systems may be controlled remotely or autonomously.

It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed system and methods without departing from the scope of the disclosure. Other embodiments of the disclosed system and methods will be apparent to those skilled in the art from consideration of the specification and practice of the system and methods disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents. 

1. A tractor scraper, comprising: a tractor portion; a scraper portion disposed rearward of the tractor portion, the scraper portion including a bowl, and an apron disposed adjacent a forward end of the bowl; and a drive configured to raise the apron, the drive including an actuator drivingly connected to a pinion; a rack connected to the apron and operably engaged to the pinion to allow the actuator to raise the apron by driving the rack with the pinion, wherein the rack is connected to the apron in a manner allowing relative movement between the rack and the apron.
 2. The tractor scraper of claim 1, wherein the rack is connected to the apron in a manner allowing pivotal relative movement between the rack and the apron.
 3. The tractor scraper of claim 2, wherein the rack is pivotally pinned to a front face of the apron.
 4. The tractor scraper of claim 1, wherein the rack is guided between the pinion and a retainer engaging a face of the rack opposite the pinion.
 5. The tractor scraper of claim 1, wherein the rack is guided in a manner restraining movement of the rack in directions parallel to the axis of the pinion.
 6. The tractor scraper of claim 1, wherein a shape of the rack differs from a shape of a vertical cross-section of the forward face of the apron.
 7. The tractor scraper of claim 1, wherein the rack has a substantially straight longitudinal axis.
 8. The tractor scraper of claim 1, wherein the rack includes a plurality of teeth facing rearward.
 9. The tractor scraper of claim 1, wherein the actuator, the pinion, and the rack are mounted to the scraper portion of the tractor scraper.
 10. The tractor scraper of claim 1, wherein the actuator is a rotary motor.
 11. A tractor scraper, comprising: a tractor portion; a scraper portion disposed rearward of the tractor portion, the scraper portion including a bowl, and an apron disposed adjacent a forward end of the bowl, the apron including a front face; and a drive configured to raise the apron, the drive including an actuator drivingly connected to a pinion, and a rack pivotally pinned to the front face of the apron, wherein the pinion is operably engaged to the rack to allow the actuator to raise the apron by driving the rack with the pinion, and wherein the rack is guided between the pinion and a retainer engaging a face of the rack opposite the pinion.
 12. The tractor scraper of claim 11, wherein a shape of the rack differs from a shape of a vertical cross-section of the forward face of the apron.
 13. The tractor scraper of claim 11, wherein the rack has a substantially straight longitudinal axis.
 14. The tractor scraper of claim 13, wherein the rack includes a plurality of teeth facing rearward.
 15. The tractor scraper of claim 11, wherein the rack includes a plurality of teeth facing rearward.
 16. A tractor scraper, comprising: a tractor portion; a scraper portion disposed rearward of the tractor portion, the scraper portion including a bowl, and an apron with a forward face disposed adjacent a forward end of the bowl; and a drive configured to raise the apron to open the forward end of the bowl, the drive including an actuator drivingly connected to a pinion; a rack connected to the apron and operably engaged to the pinion to allow the actuator to raise the apron by driving the rack with the pinion, wherein a shape of the rack differs from a shape of a vertical cross-section of the forward face of the apron.
 17. The tractor scraper of claim 16, wherein the rack has a substantially straight longitudinal axis.
 18. The tractor scraper of claim 17, wherein the rack includes a plurality of teeth facing rearward.
 19. The tractor scraper of claim 16, wherein the rack includes a plurality of teeth facing rearward.
 20. The tractor scraper of claim 16, wherein: the rack is pivotally pinned to a front face of the apron; and the rack is guided between the pinion and a retainer engaging a face of the rack opposite the pinion. 